The present invention relates to a manufacturing method for an electric wire having a terminal in which a terminal is crimped to an electric wire having a core wire bundle with a plurality of conductor core wires bundled.
Usually, from a viewpoint that an allowable electric current of an electric wire is increased and a bending strength is improved, an electric wire is proposed which has a core wire bundle (for instance, a twisted wire) with a plurality of conductor core wires bundled. When a terminal is crimped to such a core wire bundle (the twisted wire), the conductor core wire located in an outer peripheral side of the core wire bundle directly comes into contact with the terminal and is electrically connected to the terminal. However, the conductor core wire located in a central part of the core wire bundle is electrically connected to the terminal through the conductor located in the outer peripheral part of the core wire bundle. Accordingly, in order to improve an entire electric conductivity between the core wire bundle and the terminal, it is desirable that not only the electric conductivity (the electric conductivity of the outer peripheral part) between the conductor core wire and the terminal, but also the electric conductivity (the electric conductivity of the central part) between the conductor core wires is improved.
On the other hand, in recent years, aluminum and aluminum alloy may be sometimes used as a material of the conductor core wire for the reason that the aluminum and the aluminum alloy are lighter and lower in cost than copper. However, in this case, since an insulating property of an oxide film (aluminum oxide) naturally formed on a surface of the conductor core wire is high, such a contrivance as to improve the above-described electric conductivity is especially required. Specifically, it is required to improve the electric conductivity of the outer peripheral part and the electric conductivity of the central part of the core wire bundle.
Thus, for instance, in one of usual manufacturing methods for an electric wire having a terminal (refer it to as a “usual manufacturing method”, hereinafter.), an ultrasonic connection or welding process is applied to a core wire bundle (a twisted wire) formed with conductor core wires made of aluminum so that oxide films on the surfaces of the conductor core wires are broken to connect the conductor core wires together and form integrally the core wire bundle to be a single wire. Thus, both the conductor core wire located in the outer peripheral part of the core wire bundle and the conductor core wire located in the central part come into substantially direct contact with the terminal. As a result, since the electric conductivity of the central part is more improved than a case that the above-described single wire is not formed, an entire electric conductivity between the core wire bundle and the terminal may be the more improved (for instance, see patent literature 1.).
[Patent Literature 1] JP-A-2009-231079